Anyone working legally in the UK, you'd be forgiven for assuming, must be protected by the same laws; all must share the right to be paid a fair minimum wage, all must be safe from being forced to work cripplingly long hours.

You'd be wrong. Among the army of women and girls who keep the nation's homes, families and, ultimately, its economy functioning by working as cleaners, nannies and cooks, are many who are not afforded such basic rights, leaving them vulnerable to exploitation. In the worst cases, domestic workers have ended up being paid just a few hundred pounds a month for working more than 12 hours a day, seven days a week.

On Thursday, governments from around the world will vote on whether to create a new international convention aimed at protecting domestic workers from abuse, exploitation and slavery. It's a chance to make sure that the women whose labours in many cases allow middle-class women to balance careers and family life, are given the same rights as everyone else.

But to the genuine shock of campaigners, the UK has just announced it won't vote for the International Labour Organisation convention. Because it does not intend to ratify the convention – which would be necessary in order for Britain to be bound by its rules – "for the foreseeable future" it felt it could not vote in favour, according to the department for business, innovation and skills.

Charities such as Anti-Slavery International and Christian Aid had been disappointed by what they described as the obstructive role the UK's representatives played in the negotiations of the convention's text in Geneva last week, and feared getting it ratified here would be a struggle as a result. But even they did not suspect the UK would fail to support the convention at all.

Audrey Guichon, domestic work coordinator at Anti-Slavery International, says: "It is shocking that the UK government does not believe that domestic workers are 'real' workers, deserving of the same protections as everyone else.

"Not only will this decision have a negative impact on domestic workers in the UK, but it will undermine the efforts of countries ready to ratify the convention and enjoy the protections it will offer. The vast majority of countries are expected to vote in favour of this convention and the UK will be standing alone in not supporting what would be an internationally accepted minimum standard of protection of domestic workers' rights."

A spokesman for the business department says that, despite its intention not to vote for the convention, the government does "strongly support the principles it enshrines".

"The UK already provides comprehensive employment and social protections to domestic workers and we do not consider it appropriate or practical to extend criminal health and safety law, including inspections, to private households employing domestic workers," he adds.

Last week, the UK was accused of seeking to water down proposals and even isolating itself from other EU countries in its unwillingness to support key elements of the text.

Observers at the conference reported audible gasps from other delegates when Britain was the only country to oppose the proposed text of a section designed to protect domestic workers from hazards and accidents at work. Christian Aid called the UK's objection to a recommendation that governments pay special attention to the needs of child domestic workers "embarrassing".

Objecting to regulating what goes on in private homes does seems strangely old-fashioned. After all, as Guichon points out, no one would accept the argument that you shouldn't enter a household to see if a woman was being beaten up by her partner. Why on earth, you have to wonder, is domestic work not already recognised as work? Is it because it's seen as "women's work", and therefore not "proper" work?

At the moment, domestic workers in the UK are not covered by working-time regulations and if they live with their employers and are treated as "family", they're not entitled to the minimum wage – and many who are entitled are denied it anyway. Burns, cuts and other injuries are common in their roles and yet they are exempt from the protection given by health and safety legislation. Others have suffered physical, sexual or psychological abuse.